Wireless mobile communication technology uses various standards and protocols to transmit data between a node (e.g., a transmission station) and a wireless device (e.g., a mobile device). Some wireless devices communicate using orthogonal frequency-division multiple access (OFDMA) in a downlink (DL) transmission and single carrier frequency division multiple access (SC-FDMA) in an uplink (UL) transmission. Standards and protocols that use orthogonal frequency-division multiplexing (OFDM) for signal transmission include the third generation partnership project (3GPP) long term evolution (LTE) and LTE-Advanced (LTE-A), the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard (e.g., 802.16e, 802.16m), which is commonly known to industry groups as WiMAX (Worldwide interoperability for Microwave Access), and the IEEE 802.11 standard, which is commonly known to industry groups as Wi-Fi. It should be noted that LTE and LTE-A are the same technology, but LTE-A is used to distinguish releases 10 and 11 (current version) of the standard from earlier releases. Wideband Code division Multiple Access (WCDMA), a 3G technology that provides flexible voice and data services by using code division multiple access (CDMA) technology.
In 3GPP radio access network (RAN) LTE and LTE-A systems, the node can be a combination of Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Node Bs (also commonly denoted as evolved Node Bs, enhanced Node Bs, eNodeBs, or eNBs) and their associated layer-2/3 entities such as the Radio Network Controller (RNC), the Radio Resource Controller (RRC), the Media Access Controller (MAC) and parts of higher layers generically referred to as layer-2/3 . The node communicates with the wireless device, known as a user equipment (UE). Examples of a UE include a mobile terminal, a tablet computer, a personal digital assistant (PDA) and a machine-type communication (MTC) device. The downlink (DL) transmission can be a communication from the node (or eNodeB) to the wireless device (or UE), and the uplink (UL) transmission can be a communication from the wireless device to the node.
It is known in communication systems such as LTE and LTE-A, to use Multiple Input Multiple Output (MIMO) antenna configurations, which include more than one receiver and more than one transmitter to improve communication performance. MIMO spreads the total transmit power of the antennas to achieve improved the reliability of the wireless connection. MIMO results in: (a) diversity gain, which reduces the effects of fading because the receiver can take advantage of signal paths not currently experiencing fades; (b) array gain due to a beamforming effect achieved by transmitting from multiple antennas, directing the transmitted signal towards the UE; and (c) spatial multiplexing gain achieved by transmitting multiple streams of data in parallel using the same set of time and frequency resources and uncorrelated transmission paths allows the receiver to differentiate between the data streams.
In MIMO communication channels, more than one data flow from a given user or more than one user can be assigned to the same communication channel resources in frequency and time. Thus there is a requirement in the receiving apparatus to reliably separate signals corresponding to different users or corresponding to different data flows from the same user. It is known to perform interference cancellation in the receiver to improve the receiver performance in estimating transmitted signals corresponding to different users and/or different data flows. Some of these interference cancellation techniques estimate a most likely transmitted symbol sequence for a received coded message using a process known as “soft modulation”, which uses per-bit probabilities output by a decoder. There is a requirement for more efficient interference cancellation in the receiver for both uplink and downlink wireless communications.